The 3GPP (3rd Generation Partnership Project), which is a project aiming to standardize a mobile communication system, is considering to introduce a Device to Device (D2D) proximity service as a new function in Release 12 and later (see Non Patent Literature 1).
The D2D proximity service (D2D ProSe) is a service enabling direct device-to-device communication within a synchronization cluster formed by a plurality of synchronized user terminals. The D2D proximity service includes: a D2D discovery procedure (ProSe Discovery) in which a proximal terminal is discovered; and D2D communication (ProSe Communication) that is direct device-to-device communication.